Due to the very high price of tool steel, it is very desirable to have a counterbore tool in which the cutting tool can be replaced. It is also desirable to have one in which the cutting tool can be readily sharpened without changing the radius of the counterbore produced by operation of the tool.
Various arrangements have been developed for having a replacable cutting tool in a counterbore tool. The problem, however, is that it is imperative that the cutting tool be maintained rigidly against any possible movement. It is quite customary with such operations to have a tolerance of not more than 0.001 inches. It is obvious that with this low a tolerance, the cutting tool must be very accurately positioned and maintained against movement relative to the shank and pilot, particularly the latter.
It is also desirable to provide for a cutting tool which has a uniform length between its cutting edges throughout its entire width so that as the cutting tool is periodically sharpened, the length of the cutting tool and hence the size of the counterbore produced by it, will remain the same.